The field of rapid prototyping involves the production of prototype articles and small quantities of functional parts, as well as structural ceramics and ceramic shell molds for metal casting, directly from computer-generated design data.
Two well-known methods for rapid prototyping include a selective laser sintering process and a liquid binder 3D printing process. These techniques are similar, to the extent that they both use layering techniques to build three-dimensional articles. Both methods form successive thin cross-sections of the desired article. The individual cross-sections are formed by bonding together adjacent grains of a granular, (i.e., particulate) material on a generally planar surface of a bed of the granular material. Each layer is bonded to a previously formed layer at the same time as the grains of each layer are bonded together to form the desired three-dimensional article. The laser-sintering and liquid binder techniques are advantageous because they create parts directly from computer-generated design data and can produce parts having complex geometries. Moreover, 3D printing may be quicker and less expensive than machining of prototype parts or production of cast or molded parts by conventional “hard” or “soft” tooling techniques that can take from a few weeks to several months, depending on the complexity of the item.
An early 3D printing technique, described in U.S. Pat. No. 5,204,055, incorporated herein by reference in its entirety, describes the use of an inkjet style printing head to deliver a liquid or colloidal binder material to sequentially applied layers of powdered material. The three-dimensional inkjet printing technique or liquid binder method involves applying a layer of a powdered material to a surface using a counter-roller. After the powdered material is applied to the surface, the inkjet printhead delivers a liquid binder in a predetermined pattern to the layer of powder. The binder infiltrates into gaps in the powder material and hardens to bond the powder material into a solidified layer. The hardened binder also bonds each layer to the previous layer. After the first cross-sectional portion is formed, the previous steps are repeated, building successive cross-sectional portions until the final article is formed. Optionally, an adhesive may be suspended in a carrier that evaporates, leaving the hardened adhesive behind. The powdered material may be ceramic, plastic or a composite material. The liquid binder material may be organic or inorganic. Typical organic binder materials used are polymeric resins or ceramic precursors, such as polycarbosilazane. Inorganic binders can be used where the binder is incorporated into the final articles. For example, silica can be used in such an application.
It is also possible to perform ultraviolet cure of acrylate binders over particulate material. Acrylate binders provide several advantages. First of all, they are curable by ultraviolet (UV) light, thereby enabling a faster forming process than is possible with other typical curing methods. Secondly, they allow the formation of articles having surfaces with plastic appearances, thereby enabling more realistic modeling of various objects. Finally, because acrylate binders are essentially solids, no evaporation takes place after the binders are printed, thereby allowing the formation of stable, tough structures.
However, the fast curing mechanism of UV initiation of (meth)acrylate polymerization may cause excessive distortion in free flowing particulate material, resulting in curling of the printed part, which may make the printing of parts having a thickness greater than 1 millimeter exceedingly difficult. To reduce curling due to fast curing, a first printed layer may be formed on a glass build plate, adhering thereto.